The present invention relates to a constant-velocity universal joint housing.
Constant-velocity universal joints are articulated linkages for transmitting rotation between two (drive and driven) shafts, while maintaining a constant unit velocity ratio between the two shafts, regardless of the angle formed by the shaft axes, and comprise:                a core connected to one of the two shafts and having a number of radially-outward-open tracks;        a set of balls housed partly inside the tracks;        a ball retainer surrounding the core; and        a housing connected to the other of the two shafts and housing the core, retainer, and balls.        
The retainer in turn comprises:                a cup with tracks inside for housing the balls;        a male shank integral with the cup; and        a shoulder between the housing and the shank.        
In housings of the above type, the cup tapers towards the shoulder, and its larger-outer-diameter portion is bounded externally by a cylindrical outer surface used, for example, for centring for mechanical machining. The shoulder in turn is bounded externally by a cylindrical surface that substantially blends with the cylindrical outer surface of the cup, but forms a sharp change in the housing section with the cylindrical outer surface of the shank.
In actual use, e.g. in joints used in front-wheel-drive cars to connect the direction wheel hubs to the differential, the part most subject to failure and damage has proved to be the housing, precisely on account of the sharp variation in section between the shank and shoulder, which results in localized stress at the shoulder.